If you ever have need to accurately measure the true airspeed of your aircraft, I have created an android app (MeasureTAS) that makes it very simple to measure true airspeed to GPS accuracy. Basically, you fly legs in three arbitrary directions while the app captures tracks and groundspeeds and then does the calculations. The app is based on a much cited algorithm developed and published in 1998 by Doug Gray. The app is available on the Google Play Store - it is free and without ads. There is a link to Doug Gray's paper on the MeasureTAS page on Google Play.